Re: [eigen] generic argument declaration taking a matrix, vector or expression

[Martin Senst <martin.senst@xxxxxx>]

Am Donnerstag, 12. Januar 2012, 01:24:30 schrieb Benoit Jacob:
> 2012/1/11 Bernhard Zeisl <bzeisl@xxxxxxxxxxxxxxxx>:
> > Christoph, thanks a lot for your hint. That solved the problem.
> > 
> > I agree with you that with the new declaration we lost type safety.
> > Effectively A, b and x now can be of a different scalar type each.
> > While it's fine in our case that the function is templated over different
> > scalar types, it should be required that all arguments are of the same
> > type. Also it would be nice if that shows up in the interface. As of
> > now, I guess this is not possible?
> 
> As Christoph said, the only way to enforce that is by a static
> assertion, and that won't show up in the interface (if by interface
> you mean prototype). "Concepts" were supposed to make that possible
> but they got dropped from c++11, sadly.


You could use boost::enable_if to enforce that the scalar types of the 
function parameters match. The following is C++11, but it should be possible 
to make this work in C++03, too:

#define EIGEN_ENABLE_IF(condition) typename boost::enable_if_c< condition, int 
>::type = 0

#define EIGEN_ENABLE_IF_SAME_SCALAR(T1, T2) 
EIGEN_ENABLE_IF((std::is_same<typename T1::Scalar, typename 
T2::Scalar>::value))

#define EIGEN_ENABLE_IF_SAME_SCALAR3(T1, T2, T3) 
EIGEN_ENABLE_IF((std::is_same<typename T1::Scalar, typename T2::Scalar>::value 
&& std::is_same<typename T1::Scalar, typename T3::Scalar>::value))

template <typename T1, typename T2, typename T3, 
EIGEN_ENABLE_IF_SAME_SCALAR3(T1, T2, T3)>
void f(Eigen::MatrixBase<T1> t1, Eigen::MatrixBase<T2> t2, 
Eigen::MatrixBase<T3> t3);

Cheers,
Martin